1. Technical Field
The present disclosure relates to a tool for cutting into or through bone, for example during orthopaedic surgery. More particularly, but not exclusively, it relates to a tool for cutting through cortical or cancellous bone, for example to separate a joint prosthesis from surrounding bone as part of a revision procedure.
2. Prior Art
A frequently required procedure in orthopaedic surgery is revision of a joint arthroplasty, for example revision of a hip joint replacement, should an implanted prosthesis break or wear unacceptably over its articulating surface. The present disclosure will be described in relation to its use in hip joint revision, but is equally applicable to other joints and the terms “hip”, “pelvis” and “femur” may be replaced as necessary. In many cases, an implanted prosthesis is secured in a cavity within a bone, such as a femur, using polymeric organic cement such as polymethylmethacylate. Tools have been devised to soften and remove this cement and to allow convenient removal of a worn or damaged prosthesis, followed by implantation of a replacement.
However, there has been a recent increase in the use of press-fit prostheses. No cement is used to hold these in place within the femur, pelvis, etc. Instead, the implanted portions of the prostheses have porous surfaces or surfaces coated with hydroxy-apatite, which encourage ingrowth of bone, leading to stable, well-anchored implants. This formation of cancellous bone may also occasionally occur with cement-anchored implants. While not as strong as the structural bone of the wall of the femur, the pelvis or other bone, cancellous bone is not easily susceptible to cutting using the tools devised for revising cement-anchored implants, and it has become necessary to attack cancellous bone mechanically in order to revise such implants.
Furthermore, in order to remove a prosthesis, it may be necessary to remove portions of cortical bone, which cannot be achieved without using mechanical means.
A manual osteotome is effectively a specialised form of chisel, which is forced longitudinally through the bone between a prosthesis and surrounding structural bone. The force required can be so great as to compromise the directional accuracy of the technique, and may thereby damage surrounding structural bone, especially if it is weakened by osteoporosis or the like.
Another approach is to use powered burrs to drill out the bone. These may also be difficult to guide accurately, and flexure in their elongate rotating drive shafts may lead to unacceptable collateral damage in surrounding structural bone. This approach also produces inconveniently large quantities of bone swarf, which must be removed to allow clear visualisation of the point at which the burr is cutting. Furthermore, high-speed burrs lead to significant localised frictional heating, which may also harm adjacent bone, tissue or marrow.
Manual sawing through bone is a slow, tiring process, also leading to localised heating and copious bone swarf. In any case, conventional bone saws could not easily be inserted or operated between a hip or other joint prosthesis shaft and an inner wall of a femur, or between a part-spherical acetabular shell and a pelvic bone, for example.